Inbred mouse strains like AKR and C58 are high-ecotropic virus producing strains which harbor 2 or more genetic loci for infectious ecotropic virus in their genome and develop thymic T cell lymphoma in over 90% of the cases in less than a year. On the other hand, the NFS mouse which has no ecotropic viral locus in its genome has an extremely low lymphoma incidence. By introducing ecotropic viral locus from AKR or C58 into germline of NFS, several "v-congenic" (NFS-V+) strains were developed. These NFS.V+ mice develop lymphomas (>85% incidence) within 8 to 20 months of age; 90% of these are of B cell lineage. More than 700 primary tumors, transplanted samples and derivative cultured lines have been examined. Lineage origin and clonality was determined by analyses of patters of B and T cell receptor gene organization and proviral integration. These tumors rarely exhibit rearrangement of cellular genes previously described as abnormal in T or B cell tumors indicating that they should provide unique insights into the pathogenesis in B cell lineage lymphomas. Details of tumor phenotype, purpose of such studies are discussed by Dr. Hartley (Z01-AI-286). In order to study the contributions of proviral insertional mutagenesis to B cell lymphoma induction and progression we have cloned a series of somatically-acquired proviral integrations with more in progress. Non-repetitive sequences flanking the insertion are being isolated and sequenced and will be used to determine the nature of nearby genes affected by insertional mutations. Their contributions to tumor induction and progression will then be accessed through molecular analyses of the large collection of lymphoma DNAs. One of the major difficulties encountered by others in defining the effects of insertional mutations has been the lack of cell lines or frozen cells from relevant tumors to determine effects on gene expression. In the B cell lymphoma series, a substantial number of tumors examined for their viral content exist as frozen cells, cell lines passaged in SCIDs or Rag knockout mice, and less often as cultured cell lines. Most of the somatically acquired integrations under study occured in tumors with this type of history. In addition, we are examining integrations occuring in lymphomas of NIH swiss mice induced by a possible new lymphomagenic MuLV isolate (see also Z01-AI-284).